The present invention relates to a tennis racket. More particularly, the present invention relates to a lightweight tennis racket for regulation-ball tennis having improved restitution performance, ball controllability, and vibration-damping performance.
The so-called “thick racket” which is thick in the out-of-plane direction of the racket frame is commercially available. Female and senior tennis players require the “thick racket” because they desire the tennis racket to have highs ball rebound performance, even though they hit the ball with a small amount of power. That is, they demand a tennis racket that is light in weight and has a high, ball rebound performance. Therefore a fiber reinforced resin is mainly used as the material for the tennis racket because the fiber reinforced resin has a light weight, has a high specific strength, and provides a high degree of freedom when designing the tennis racket.
However, the light weight tennis racket has a the problem that in the collision between the tennis racket and the ball, the coefficient of restitution of the ball becomes low according to the law of energy conservation. That is, to make the tennis racket lightweight causes the rebound performance to deteriorate. To solve this problem, it is possible to enhance the moment of inertia of the tennis racket in the swing direction by placing the center of gravity thereof at a position a little closer to the top of the racket frame. However, when the moment of inertia of the tennis racket in the swing direction is large, the player feels that the tennis racket is heavy and thus its operability deteriorates.
The light weight tennis racket causes the impact applied thereto when the ball is hit to be readily transmitted to a player's hand, which causes the player to suffer from tennis elbow. Thus, both female and senior tennis players who participate in competitions requires a tennis racket which has a high face stability and excellent controllability and is light weight.
To solve these problems, the present applicant proposed a tennis racket disclosed in Japanese Patent Application Laid-Open No. 2003-175134 (patent document 1). The present applicant developed a tennis racket whose rebound performance, operability, and face stability are improved in a favorable balance by enhancing the rigidity of the racket frame and setting the ratio between the swing-direction moment of inertia affecting the rebound performance thereof and the center-direction moment of inertia affecting the face stability thereof to a predetermined range.
However, in the tennis racket shown in patent document 1, attention was not paid to an improvement of its vibration-absorbing performance.
In Japanese Patent Application Laid-Open No. 2000-300698 (patent document 2), as shown in FIG. 19, the string protection member 2 is constructed of a vibration-damping member 3 in which the cylindrical portion 3a through which strings are inserted and the belt-shaped portion 3b connected with the cylindrical portion 3a; and the belt-shaped protection member 4 covering the periphery of the belt-shaped portion 3b of the vibration-damping member 3. The weight member 5, made of a material having a specific gravity of not less than 1.5 and the vibration-damping member 3 are mounted on the racket frame 1 by holding down the weight member 5 and the vibration-damping member 3 with the protection member 4. Accordingly, the tennis racket exhibits improved rebound performance, face stability, and vibration-absorbing performance.
However, the tennis racket shown in patent document 2 is not constructed to increase the deformation amount of the string protection member 2. Thus the rebound performance of the racket frame cannot be effectively improved, and its ball-flying performance cannot be enhanced. Another problem with this tennis racket is that the number of component parts increases which makes it difficult to achieve a light weight. Thereby the operability of the tennis racket may deteriorate.
In addition to the means disclosed in the above patent documents, the following rebound performance-improving means are conceivable:
(1) The area of the face of the racket frame is increased to widen the string-movable range.
(2) The in-plane rigidity of the frame is increased.
(3) The elasticity of the frame is made high.
However, means (1) has the problem that because the area of the face is increased, the weight and the moment of inertia of the tennis racket is increased and hence its operability deteriorates. Means (2) has the problem that the moldability deteriorates due to the alteration of the sectional configuration of the frame caused by the formation of a layered construction or a reinforcing portion. Means (3) has a the problem that the strength of the frame deteriorates.
Patent document 1: Japanese Patent Application Laid-Open No. 2003-175134
Patent document 2: Japanese Patent Application Laid-Open No. 2000-300698